1. Field of the Invention
The invention relates to pitch change apparatus and systems for aircraft gas turbine engine counter-rotatable propellers and, more particularly, to such apparatus and systems for pitch change actuation across an exhaust flowpath.
2. Description of Related Art
One type of aircraft gas turbine engine includes a power turbine driving counter-rotatable propeller rotors and the power turbine is powered by a gas generator. A pitch change actuation system including a hydraulic fluid delivery system is used for pitch change actuation of counter-rotatable propellers mounted on the counter-rotatable propeller rotors. The pitch change system includes pitch change actuators mounted in counter-rotatable frames which also support the counter-rotatable propellers and blades.
Rotating change actuators and gearing are subject to centrifugal loading. The propellers may be mounted radially outwardly of a flowpath and actuators and gearing mounted radially outwardly of the flowpath are subject to greater centrifugal loading. Such designs can prove to be difficult as it is hard to supply and scavenge oil near the outer flow path. Also, the additional weight of gearing at such a high radius above center line causes large centrifugal forces on the rotor structure that must be dealt with.
Thus, it is highly desirable to provide a powerful robust and quick acting hydraulic pitch actuation for the counter-rotatable propeller rotors that is lighter and more robust than that of current designs.